We propose studies to examine those interactions between certain animal viruses and their host cells which result in selective interference with protein synthesis directed by either cellular or viral messenger RNAs. As an example of virus-induced inhibition of cellular protein synthesis, we are utilizing poliovirus infection of cultured HeLa cells, which results in a rapid disaggregation of host cell polysomes prior to the formation of poliovirus-specific polysome and uninhibited translation of viral mRNA. Cellular RNA synthesis has been shown to occur, but translation is blocked at the level of initiation. The untranslated mRNA is structurally intact, polyadenylated, capped and methylated, and can be shown to function normally in vitro after extraction from infected cells. We are examining both cellular and viral protein synthesis in vitro to determine the differences in requirements for host cell and viral protein synthesis and to analyze the factors causing restriction. We hope to understand the mechanisms by which selectivity for different mRNAs can be imposed on protein synthesis. BIBLIOGRAPHIC REFERENCE: Helentjaris, T. and Ehrenfeld, E. (1977). Inhibition of Host Cell Protein Synthesis by UV-Inactivated Poliovirus. J. Virol. 21, 259-267.